In this paper orbits are assessed for their relative attractiveness based on various factors. First, a set of constraints related to the capability of the combined Orion and SLS system to deliver humans and cargo to and from the orbit are evaluated. Second, the ability to support potential lunar surface activities is considered. Finally, deployed assets intended to spend multiple years in the Proving Ground would ideally require minimal station keeping costs to reduce the mass budget allocated to this function. Additional mission design drivers include potential for uninterrupted communication with deployed assets, thermal, communications, and other operational implications.

The paper analyzes 7 orbits—Low Lunar Orbit, Prograde Circular, Frozen Lunar Orbit, Elliptical Lunar Orbit, Near-Rectilinear Orbit, Earth-Moon L2 Halo, and Distant Retrograde Orbit—and how each fits the criteria above. Jonathan Goff also did a similar exploration on the usefulness of these orbits, but his was specifically focused on an architecture involving LEO and lunar depots.

The best balance was found to be NRO for its relatively easy access from Earth, fast and global access to the lunar surface, low stationkeeping needs, constant communication with Earth (and good communication coverage of the lunar surface), among a handful of other advantages. That answers the “Why NRO?” question, and leads us into…

Why build the Gateway?

The Deep Space Gateway and Transport, and the way they were announced, are pretty symbolic of the limbo NASA is stuck in when it comes to long-term plans. Is the Deep Space Gateway meant to be a stepping stone to Mars? Should it be on the critical path to Mars? Or should it be a project in its own right, with focus to suit?

If NASA was focused solely on getting to Mars, they would skip the DSG and instead put the money towards DST off the bat. But the choice of NRO and the existence of DSG tip their hand. They want to build up a presence around the Moon, with surface access as a priority.

The most recent OIG report (PDF, 6.7MB) stresses the importance cost sharing to NASA’s plans. That means finding international and commercial partners willing to help foot the bill. Surface access is exactly where NASA intends to share costs.

NASA could focus on getting their own budget to cover the build up of the DSG through the 2020s, and let ESA—with their interest in the Moon Village concept—and commercial partners like Blue Origin—with their Blue Moon lander—cover the rest of the trip to the surface.

The way the pieces are aligning, it sure seems like NASA is headed back to the Moon, with no regard for Mars. The hand-wavy reference to the Deep Space Transport is probably there only to ease the transition, politically, away from Mars and back towards the Moon. The other remaining wrinkle in the plan: the giant ISS budget.

What NASA needs, as it has always needed, is focus. Being stuck in limbo about where the program is headed in a decade—while still spending billions on the ISS per year—is completely counter-productive. If the Moon is the destination, make it official, let the ISS burn up in 2024, and get on with the DSG.

Personally, I think the Moon is a much more achievable destination given the political environment we find ourselves in today. There is enough interest between NASA, ESA, and the private sector that the focus and clarity brought about by this plan could plant the seeds of a real, thriving economy in cislunar space.

And if you’re someone who believes Mars should be the goal, then you’ll be happy to know that there will be plenty of contracts to be had, services to be sold, and work to be done in cislunar space. SpaceX will almost certainly win more than a few, which would help bolster their own ambitions, just as the current ISS contracts have done.

Regardless of how you think our collective plans should be organized, we can all agree that we’d rather see something happen. Let’s be honest about where we’re headed, and get on with it.

Momentum is more important than the particulars of any given plan. It’s why the 20 years between Yuri and Shuttle are so incredible to look back on, and why the 30 years after that seem so dry.